In Fig. REF , we plot the parameters determining the spin distributions, as defined in Eq. (REF ), for our default model.
In Fig. REF  we plot the equivalent spin population hyperparameters for the model with \(\lambda _0 = 0\) , and in Fig. REF  we plot the spin population hyperparameters when using a uniform prior for \(m_\mathrm {max}\) .
The \(m_\mathrm {max}\)  prior makes negligible difference to the spin distributions.
There is no simple correlation between the fraction of 1G+1G  binaries with zero spin \(\lambda _0\)  and the other population hyperparameters.
The \(\lambda _0\)  distribution is peaked at 0 and shows that many 1G+1G  binaries are not well described by both black holes having near-zero spins.
In all cases we favor models with \(\alpha _\chi < \beta _\chi \) , which corresponds to distributions which decrease with increasing spin magnitude [1]}, [2]}.
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